For example, music distribution services for distributing music via the Internet are known. In such a music distribution service, encoded data obtained by encoding an audio signal of music or the like is distributed, and a technique of removing a high band component of the audio signal and encoding only a remaining low band component is used to compress a data amount of the encoded data.
However, when the audio signal encoded by this technique is decoded and reproduced, since the high band component included in an original signal has been lost, a sense of realism of the original sound is lost, and deterioration in audio quality in which sound is indistinct is likely to occur.
In this regard, a band expansion technique of generating a signal of a wide frequency band by generating a high band component from a signal of a low band component and adding the obtained high band component to the signal of the low band component was proposed (for example, see Patent Literature 1).